In chemical processing industries, such as the semiconductor industry, pneumatic and other types of actuated valves are typically used to distribute and/or control the flow of process liquids and gases from one location to another or from one piece of process equipment to another. From time to time, the equipment which is fed by fluid flowing through such valves must be shutdown, isolated, and taken out of service for maintenance, upgrading, or other reasons. For safety reasons, when such equipment is taken out of service, it is desirable that it be isolate from the process fluid normally flowing to it.
While many valves placed in such service are designed having a fail-closed feature. Due to the oftentimes aggressive chemical nature of the process fluids being used in many fluid transport applications it is usually not enough to simply rely on the fail closed feature of the valve to ensure that flow of liquid through it will not occur. Therefore, the task of isolating a downstream piece of equipment can be problematic if a secondary valve, e.g., a block valve, is not already installed within the fluid transport system.
Additionally, in the event that the valve is a three-way valve providing outlet fluid flow to two different pieces of equipment, the situation of isolating the piece of equipment must be handled in a manner that will enable it to be isolated while also permitting the value to continue its distribution of fluid to the other in service downstream device.
As briefly mentioned above, one solution that has been used to address the foregoing problem is to add one or more secondary valves, especially manually actuated valves, in line with the pneumatic valve. Such secondary valve can be installed upstream or downstream from valve, in the event that the valve has a single inlet and single outlet, or can be installed downstream from the valve in the event that the valve have more than one outlet and it is desired that one of the outlet feed stream remain on line. The secondary valves are manually closed to isolate the out-of-service equipment to ensure closure of fluid flow from the valve. When three-way fluid transport valves are used, the secondary valves may be placed on both fluid outlets to allow their respective pieces of equipment to be manually blocked in.
The use of such secondary valves is undesirable for several reasons. First, if the fluid flow system does not already have such valves in place, it is an additional cost in terms of the valves themselves, their installation, and the process down time to have the valves installed. Second, the presence of such secondary valves in a fluid transport system tends to increase the frictional losses within the system (even when they are wide open), thereby increasing the system pressure drop, reducing fluid transport efficiency and increasing pumping costs. Third, the secondary valves, like any other piece of fluid transfer equipment, requires maintenance that also contribute to increased capital and labor expenditures, and that can possibly contribute to unintended process shutdowns.
It is, therefore, desirable that a fluid transport valve be constructed in a manner that enables it to both function as an actuated valve to control fluid flow therethrough to a downstream fluid transport piece of equipment, while at the same time be capable of being operated or positioned into a closed or shut off position that is sufficiently reliable to enable the downstream piece of equipment to be isolated without the need for additional intervening secondary valves or the like. It is further desired that such fluid transport valve be configured in a manner that is space efficient, to permit its fitment within new and/or existing fluid transport systems without adversely impacting the same